diff --git a/ast.ml b/ast.ml
index ae18fa3..9f3905c 100644
--- a/ast.ml
+++ b/ast.ml
@@ -30,14 +30,9 @@ module Value = struct
   let to_string = function
     | Int n -> string_of_int n
     | Float n -> string_of_float n
-    | String s -> s
+    | String s -> "\"" ^ s ^ "\""
     | Nop -> "nop"
 
-  let of_token = function
-    | Token.Int n -> Int n
-    | Float n -> Float n
-    | _ -> invalid_arg "Value.of_token"
-
   let typeof = function
     | Int _ -> Type.Int
     | Float _ -> Type.Float
diff --git a/lex.ml b/lex.ml
index 48a6ad4..93afc86 100644
--- a/lex.ml
+++ b/lex.ml
@@ -1,6 +1,9 @@
+open Ast.Value
+
 type tokens = Token.t Seq.t
 
 exception Token_not_found
+exception Unclosed_quote
 
 let either f g c =
   f c || g c
@@ -58,24 +61,37 @@ let tokenize (str : string) : tokens =
     let open Token in
     match seq () with
     | Seq.Nil -> Seq.Nil
-    | Seq.Cons (x, s) ->
+    | Seq.Cons (x, seq) ->
       if is_whitespace x then
-        aux s () (* skip whitespace *)
+        aux seq () (* skip whitespace *)
+
+      else if x = '"' then
+        let str, seq = partition_while ((<>) '"') seq in
+        let str = String (String.of_seq str) in
+        begin match seq () with
+          | Seq.Nil -> raise Unclosed_quote
+          | Seq.Cons (x, seq) ->
+            if x = '"' then Seq.Cons (Value str, aux seq)
+            else raise Unclosed_quote
+        end
+
       else if is_digit x then
-        let n, s = partition_while is_num s in
+        let n, seq = partition_while is_num seq in
         let n = String.of_seq @@ Seq.cons x n in
         let n =
           if String.contains n '.' (* float *)
           then Float (float_of_string n)
           else Int (int_of_string n)
         in
-        Seq.Cons (n, aux s)
+        Seq.Cons (Value n, aux seq)
+
       else if is_ident_start x then
-        let id, s = partition_while is_ident seq in
-        let id = String.of_seq id in
-        Seq.Cons (Ident id, aux s)
+        let id, seq = partition_while is_ident seq in
+        let id = String.of_seq @@ Seq.cons x id in
+        Seq.Cons (Ident id, aux seq)
+
       else
-        match find_token seq with
+        match find_token @@ Seq.cons x seq with
         | None -> raise Token_not_found
         | Some (t, s) -> Seq.Cons (t, aux s)
   in
diff --git a/main.ml b/main.ml
index 8bdcad8..f5ede32 100644
--- a/main.ml
+++ b/main.ml
@@ -7,6 +7,7 @@ let version = "%%VERSION%%"
 let error_to_string e =
   try raise e with
   | Lex.Token_not_found -> sprintf "invalid token"
+  | Lex.Unclosed_quote -> sprintf "string not closed"
   | Parser.Expected t -> sprintf "expected %s" t
   | Parser.Unexpected_token t -> sprintf "unexpected token \"%s\"" t
   | Ast.Invalid_type t -> sprintf "invalid type %s" (Ast.Type.to_string t)
diff --git a/parser.ml b/parser.ml
index 1492822..9f412f0 100644
--- a/parser.ml
+++ b/parser.ml
@@ -173,8 +173,7 @@ and value seq =
   match seq () with
   | Seq.Nil -> raise End_of_tokens
   | Seq.Cons (x, seq) -> begin match x with
-      | Token.Int n -> Value (Int n), seq
-      | Float n -> Value (Float n), seq
+      | Token.Value x -> Value x, seq
       | Ident id -> Var id, seq
       | LParen ->
         let e, seq = expr min_int seq in
diff --git a/token.ml b/token.ml
index 3647f3c..6c28600 100644
--- a/token.ml
+++ b/token.ml
@@ -1,6 +1,5 @@
 type t =
-  | Int of int
-  | Float of float
+  | Value of Ast.Value.t
   | Ident of string
   | Plus
   | Minus
@@ -25,8 +24,7 @@ let tokens = ref [
 ]
 
 let to_string = function
-  | Int n -> Printf.sprintf "[int: %d]" n
-  | Float n -> Printf.sprintf "[float: %f]" n
+  | Value v -> Ast.Value.to_string v
   | Ident s -> s
   | t ->
     begin match List.find_opt (fun (_, tok) -> t = tok) !tokens with